Split Planar Transformer Layout for Common-Mode EMI Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing RF transformers in isolated DC-DC converters suffer from asymmetry in parasitic capacitance distribution across the isolation barrier, leading to undesirable electromagnetic interference (EMI) due to common mode dipole emission.
Innovation Solution
A symmetric split planar transformer design is introduced, where the primary winding is split into at least two coils with equal capacitive coupling to the secondary winding, reducing asymmetry and EMI. Each coil includes stacked spiral portions in multiple metal planes to enhance inductive density and opposite spiral directions to minimize far-field radiation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a conventional transformer with a single primary winding is used, then the structure is simple, but asymmetry in parasitic capacitance distribution causes common mode EMI
Solution Approach 1:
The primary winding is segmented into multiple coils (first coil and second coil) with equal capacitive coupling to the secondary winding. This segmentation creates symmetry in parasitic capacitance distribution, thereby reducing common mode EMI while maintaining functional simplicity
2Object-affected harmful factors
If the primary winding is split into multiple coils to reduce EMI, then common mode EMI is reduced, but the device complexity increases
Solution Approach 1:
The patent applies asymmetry principle by creating a symmetric structure through asymmetric design - splitting the primary winding into multiple coils with equal capacitive coupling to achieve symmetry in parasitic capacitance distribution, thereby reducing common mode EMI
3Quantity of substance
If standard planar transformer design is used, then manufacturing is easier, but inductive density is insufficient
Solution Approach 1:
The patent transitions from planar 2D coil structures to 3D stacked spiral portions in multiple metal planes. This dimensional change increases inductive density by utilizing vertical stacking while maintaining compatibility with standard planar manufacturing processes
4Power
If coils are designed to maximize inductive coupling, then power transfer efficiency improves, but far-field radiation increases
Solution Approach 1:
The patent uses opposite spiral directions for adjacent coils, creating asymmetric current paths that generate opposing magnetic fields. These opposing fields cancel each other out, reducing far-field radiation while maintaining effective inductive coupling for power transfer
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The symmetric split planar transformer effectively reduces common mode EMI by balancing capacitive coupling, enhancing inductive density, and minimizing far-field radiation, thereby improving the performance of isolated DC-DC converters.
Implementation Method 1
A transformer is typically used to couple two sides of an electrical system, sometimes called a primary side and a secondary side. The two sides are often electromagnetically coupled
Implementation Method 2
the electric field across the isolation barrier may be represented by capacitors across the barrier
Data Source
Figure 1
Figure 2A~2B
Figure 3
AI summary
Disclosed herein is a symmetric split planar transformer in the context of a DC-DC isolated converter. The symmetric split planar transformer reduces or eliminates asymmetry in the distribution of parasitic capacitance across the isolation barrier going from one end to another end of a primary coil, and as a result, undesirable electromagnetic interference (EMI) due to common mode dipole emission across the isolation barrier may be reduced. In some embodiments, the primary winding is split into at least a first coil (1010) and a second coil (1020), each occupying a different area (S1, S2) side-by-side on a substrate (1090). The transformer is symmetric in the sense that a capacitive coupling of the first coil to a secondary winding is the same as a capacitive coupling of the second coil to the secondary winding, such that common mode EMI may be reduced. Each coil may include stacked spiral coil portions in multiple metal planes to increase inductive density across the isolation barrier. Furthermore, in some embodiments the first and second coils may have opposite spiral directions such that far field radiation effect from the transformer may be reduced.